The present application is based on and claims priority from Japanese Patent Application 2002-261846, filed Sep. 6, 2002, the contents of which are incorporated herein by reference.
1. Field of the Invention
The present invention relates to an electric motor and a method and an apparatus for manufacturing such a motor.
2. Description of the Related Art
Usually, a motor has a stator that includes a plurality of permanent magnets circumferentially disposed on the inside surface thereof to provide magnetic poles and a rotor that is disposed in the space surrounded by the magnetic poles. For example, JP-A-10-145990 discloses a motor in which the rotor is constituted of a center core, a plurality of coil cores on which concentrated coils or solenoid coils are mounted. The center core is disposed to be coaxial with the rotating axis of the rotor, and the coil cores are disposed around the center core. Each of the concentrated coils is wound around an insulator. Thus, a high space factor, which is a ratio of the conductor""s volume to the motor""s total volume, can be provided.
In the disclosed motor, the center core and the coil cores are fixed by means of concavity-convexity connection. In other words, projections are formed in one of the center core and the coil cores, and recesses are formed in the other so that the projections can be fitted into the recesses in the radial direction when they are assembled.
However, it is difficult to insert a plurality of projections into the recesses at one time, and each coil core has to be fixed to the center core.
A main object of the invention is to provide an improved rotor of a motor that is easy to be assembled.
According to a main feature of the invention, a motor includes a permanent magnet unit disposed at a circumference for providing a plurality of magnetic poles, a rotor disposed inside the circumference to be coaxial with the permanent magnet unit. The rotor is constituted of a center core disposed to be coaxial with a center axis of the rotor, a plurality of coil cores disposed at peripheral portions of the rotor and a plurality of concentrated coils respectively mounted on the coil cores. In assembling, each coil core is fitted to the center core by sliding in an axial direction of the center core.
In the above featured motor, one of the center core and the plurality of coil cores has axially extending engagement grooves at peripheral portions thereof, and the other has axially extending engagement projections at peripheral portions thereof. The engagement projections project toward the engagement grooves to be fitted to the engagement grooves when the engagement projections move or slide in the axial direction. Preferably, the engagement groove has a generally trapezoidal cross-section having a smaller parallel side being open at the peripheral portion, and the engagement projection has a generally trapezoidal cross-section that is complementary to the trapezoidal cross-section of the engagement groove.
In the above featured motor, an axial end of the engagement groove or an axial end of the engagement projection is chamfered.
Another object of the invention is to provide a method of manufacturing such an improved motor.
Another main feature of the invention, a method of manufacturing the above featured motor includes a step of holding a plurality of coil cores disposed in the same position as the rotor so that the periphery thereof can be on a prescribed circle, and a step of moving the center core in the axial direction thereof to insert the same into the inside surfaces of the coil cores.
In the above featured method of manufacturing, the step of moving further includes a step of restricting the coil cores to move in radially outward directions. Preferably, the step of restricting includes a step of pressing the coil cores in radially inward directions. The step of holding may include a step of restricting the coil cores to move in an axial direction of the prescribed circle, and the step of moving may include a step of pressing an axial end of the center core in the same axial direction to insert the center core into the coil cores.
Another object of the invention is to provide an apparatus for manufacturing such an improved motor.
According to another feature of the invention, an apparatus for manufacturing the above featured motor includes means for holding the plurality of coil cores disposed in the same position as the rotor so that the periphery thereof can be on a prescribed circle, and means for moving the center core in the axial direction thereof to insert the same into the inside surfaces of the coil cores. In the above featured apparatus, the means for of moving may include means for restricting the coil cores to move in radially outward directions. In the above featured apparatus, the step of restricting may include means for pressing the coil cores in radially inward directions. The means for holding may include means for restricting the coil cores to move in an axial direction of the prescribed circle, and the means for moving may include means for pressing an axial end of the center core in the same axial direction to insert the center core into the coil cores.